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b-coloring is NP-hard on co-bipartite graphs and polytime solvable on tree-cographs

Identifieur interne : 005444 ( Hal/Curation ); précédent : 005443; suivant : 005445

b-coloring is NP-hard on co-bipartite graphs and polytime solvable on tree-cographs

Auteurs : Flavia Bonomo [Argentine] ; Oliver Schaudt [France] ; Maya Stein [Chili] ; Mario Valencia-Pabon [France]

Source :

RBID : Hal:hal-01102516

Abstract

A b-coloring of a graph is a proper coloring such that every color class contains a vertex that is adjacent to all other color classes. The b-chromatic number of a graph G, denoted by \chi_b(G), is the maximum number t such that G admits a b-coloring with t colors. A graph G is called b-continuous if it admits a b-coloring with t colors, for every t = \chi(G),\ldots,\chi_b(G), and b-monotonic if \chi_b(H_1) \geq \chi_b(H_2) for every induced subgraph H_1 of G, and every induced subgraph H_2 of H_1. We investigate the b-chromatic number of graphs with stability number two. These are exactly the complements of triangle-free graphs, thus including all complements of bipartite graphs. The main results of this work are the following: - We characterize the b-colorings of a graph with stability number two in terms of matchings with no augmenting paths of length one or three. We derive that graphs with stability number two are b-continuous and b-monotonic. - We prove that it is NP-complete to decide whether the b-chromatic number of co-bipartite graph is at most a given threshold. - We describe a polynomial time dynamic programming algorithm to compute the b-chromatic number of co-trees. - Extending several previous results, we show that there is a polynomial time dynamic programming algorithm for computing the b-chromatic number of tree-cographs. Moreover, we show that tree-cographs are b-continuous and b-monotonic.

Url:
DOI: 10.1007/s00453-014-9921-5

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<div type="abstract" xml:lang="en">A b-coloring of a graph is a proper coloring such that every color class contains a vertex that is adjacent to all other color classes. The b-chromatic number of a graph G, denoted by \chi_b(G), is the maximum number t such that G admits a b-coloring with t colors. A graph G is called b-continuous if it admits a b-coloring with t colors, for every t = \chi(G),\ldots,\chi_b(G), and b-monotonic if \chi_b(H_1) \geq \chi_b(H_2) for every induced subgraph H_1 of G, and every induced subgraph H_2 of H_1. We investigate the b-chromatic number of graphs with stability number two. These are exactly the complements of triangle-free graphs, thus including all complements of bipartite graphs. The main results of this work are the following: - We characterize the b-colorings of a graph with stability number two in terms of matchings with no augmenting paths of length one or three. We derive that graphs with stability number two are b-continuous and b-monotonic. - We prove that it is NP-complete to decide whether the b-chromatic number of co-bipartite graph is at most a given threshold. - We describe a polynomial time dynamic programming algorithm to compute the b-chromatic number of co-trees. - Extending several previous results, we show that there is a polynomial time dynamic programming algorithm for computing the b-chromatic number of tree-cographs. Moreover, we show that tree-cographs are b-continuous and b-monotonic.</div>
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<forename type="first">Maya</forename>
<surname>Stein</surname>
</persName>
<idno type="halAuthorId">1115299</idno>
<affiliation ref="#struct-227891"></affiliation>
</author>
<author role="aut">
<persName>
<forename type="first">Mario</forename>
<surname>Valencia-Pabon</surname>
</persName>
<idno type="halAuthorId">111523</idno>
<affiliation ref="#struct-994"></affiliation>
<affiliation ref="#struct-205125"></affiliation>
</author>
</analytic>
<monogr>
<idno type="halJournalId" status="VALID">10334</idno>
<idno type="issn">0178-4617</idno>
<idno type="eissn">1432-0541</idno>
<title level="j">Algorithmica</title>
<imprint>
<publisher>Springer Verlag</publisher>
<biblScope unit="pp">17</biblScope>
<date type="datePub">2014</date>
</imprint>
</monogr>
<idno type="doi">10.1007/s00453-014-9921-5</idno>
<idno type="arxiv">1310.8313</idno>
</biblStruct>
</sourceDesc>
<profileDesc>
<langUsage>
<language ident="en">English</language>
</langUsage>
<textClass>
<classCode scheme="halDomain" n="math">Mathematics [math]</classCode>
<classCode scheme="halDomain" n="info">Computer Science [cs]</classCode>
<classCode scheme="halTypology" n="ART">Journal articles</classCode>
</textClass>
<abstract xml:lang="en">A b-coloring of a graph is a proper coloring such that every color class contains a vertex that is adjacent to all other color classes. The b-chromatic number of a graph G, denoted by \chi_b(G), is the maximum number t such that G admits a b-coloring with t colors. A graph G is called b-continuous if it admits a b-coloring with t colors, for every t = \chi(G),\ldots,\chi_b(G), and b-monotonic if \chi_b(H_1) \geq \chi_b(H_2) for every induced subgraph H_1 of G, and every induced subgraph H_2 of H_1. We investigate the b-chromatic number of graphs with stability number two. These are exactly the complements of triangle-free graphs, thus including all complements of bipartite graphs. The main results of this work are the following: - We characterize the b-colorings of a graph with stability number two in terms of matchings with no augmenting paths of length one or three. We derive that graphs with stability number two are b-continuous and b-monotonic. - We prove that it is NP-complete to decide whether the b-chromatic number of co-bipartite graph is at most a given threshold. - We describe a polynomial time dynamic programming algorithm to compute the b-chromatic number of co-trees. - Extending several previous results, we show that there is a polynomial time dynamic programming algorithm for computing the b-chromatic number of tree-cographs. Moreover, we show that tree-cographs are b-continuous and b-monotonic.</abstract>
</profileDesc>
</hal>
</record>

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